This invention relates to gas burner controls for furnaces and the like, and in particular to a new and improved pilot burner gas igniter and main burner valve controller. The system utilizes a pilot burner flame sensor and a fast responding solid state electronic control circuit for switching the main burner solenoid valve and the pilot burner spark igniter circuit.
A typical system of this type is energized when the electrical contacts of a thermostat close in response to a drop in temperature of the area being heated by the gas furnace. When the thermostat switch closes, the pilot burner valve is opened and the spark igniter circuit provides sparking at the pilot igniter electrodes and the gas at the pilot burner should ignite. The flame sensor and control circuit detects the existence of the flame and actuates a switching circuit to energize the main burner valve and turn off the spark igniter circuit. If flame outage occurs, the flame sensing circuitry will detect the absence of flame and close the main burner valve, while at the same time turning on the spark igniter for reigniting the pilot burner.
Systems of this general type are known. One type of prior art system omits the pilot burner, placing the igniter and sensor at the main burner. However, this type of system is usually considered unsatisfactory for larger capacity burners because of the possibility of explosion resulting from accumulation of gas prior to ignition. Another type of prior art system does not utilize the spark igniter, maintaining the pilot burner on at all times. However this type of system is undesirable because of the waste of gas with the continuously burning pilot.
The most pertinent prior art system presently known to applicant is the Penn Baso cycling pilot ignition system Series G60. In this system, closing of the thermostat switch energizes the solenoid of the pilot burner valve and the spark igniter circuit to produce the pilot flame. The pilot flame is sensed and utilized in a control circuit for actuating a relay to energize the main burner valve solenoid and turn off the spark igniter circuit. The furance control systems normally are operated from a 24 volt ac source. However, this prior art system requires a 100 volt ac supply, with the flame sensor, the control circuit and the relay being operated from the 100 volt secondary of a voltage step-up transformer.
Another prior art system is shown in U.S. Pat. No. 3,619,097. This sytem omits the pilot burner and utilizes the flame sensor for controlling the main burner valve solenoid and the spark ignition circuit. This prior art system also requires a 100 volt ac supply for the control, switching and spark igniter circuits.
Two other prior art systems are shown in U.S. Pat. Nos. 3,574,496 and 3,610,790. The first patent describes a more complex system which operates from a 100 volt source and utilizes a flame rod sensor and a flame ultraviolet sensor, while omitting the pilot burner. The second patent shows another complex system which omits the pilot burner and utilizes one of the spark ignition electrodes as the flame sensor.
It is an object of the present invention to provide a new and improved furnace control system having improved sensitivity and fast response to flame outage and operable at relatively low voltage with a resultant saving in cost and electrical insulation problems. A further object is to provide such a system suitable for high capacity burners and utilizing a pilot burner, and one which has a fail safe characteristic for all components of the system.